An Ionic liquid is a salt in a liquid state at normal temperature and is characterized in that its vapor pressure is as close to zero as possible and its liquid state is kept even if it is heated and is in vacuum. To use this characteristic for operation and observation in a vacuum chamber has been considered.
Patent Literature 1 discloses a charge-up prevention liquid medium for an electronic microscope, which is composed of a cation and an anion, and an ionic liquid as an essential component and is impregnated in an entire sample for a scanning type electronic microscope (SEM) or an entire sample for a transmission type electronic microscope (TEM), or is applied onto an electron irradiation surface thereof, and imparts electroconductivity to the electron irradiation surface.
Moreover, Patent Literature 2 discloses a device which is provided with an ionic liquid storage tank, an electron spray device having a needle-shaped conductive capillary, and an ionic liquid recovery device, and emits a solution containing an ionic liquid into a gas phase using an electro spray method and generates an ion beam.